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Farmer: You never know who might be watching

The ancients knew them as the wanderers, those five bright stars that travel across the heavens like cosmic mariners. Today they are known by their Roman names — Mercury, Venus, Mars, Jupiter and Saturn.

With the invention of the telescope in the 17th century they have since been joined by Uranus, Neptune and the recently humbled Pluto, now officially known as a “dwarf planet.” Perhaps this ignominious demotion in stature is justified when one considers that Pluto is smaller than our own moon and may itself be an escaped satellite of Neptune.

Then there is Earth, that third rock from the sun, home to all humanity and, as far as we are aware, every living thing in the universe. Many consider Earth to be a privileged planet, singularly unique in all the cosmos. The idea that our tiny home planet was somehow the very center of the universe took a big hit in 1543 when Nicolaus Copernicus demonstrated that Earth was just like the other planets. It, too, slowly circles our sun in an orderly and regular journey that we call a year.

It would take nearly 150 years for most people to accept that the sun, and not the Earth, lay at the center of our corner of the universe. The astronomer Galileo nearly paid with his life in his defense of this truth.

Since then, most of us have been content in the belief that it was our sun, and our planet, that were chosen to be the cradle of life. Yet here in the 21st century, we must now come to terms with another sobering realization. We are almost certainly not alone.

In 1995, the first planet outside of our own solar system was discovered. This “exoplanet” was much larger than Earth. Like Jupiter and Neptune, it is not solid, but is made of gas. It also circled its home star at the frantic pace of once every four days. Still, the idea that other stars harbored their own host of companion planets raised the possibility that Earth, and we, are not quite as unique as we once thought.

More than 700 exoplanets have now been discovered, and the pace of their discovery is accelerating. Launched in 2009, NASA’s Kepler Space Observatory has identified 33 confirmed exoplanets and nearly 2,400 potential targets. In early December, NASA announced the discovery of two Earth-sized planets, orbiting a star much like our sun. They join Gliese 581 d, an unconfirmed exoplanet that may lie in the habitable zone of its star, meaning that liquid water may fill its oceans, rivers and lakes.

It now seems only a matter of time before we learn of a true Earth-like planet. The relative ease with which we have found exoplanets has led some astronomers to predict that as many as 10 percent of all stars have planets that can sustain life. A raised thumb held against the night sky blocks the light of more than 4,000 galaxies, each with over 100 billion stars. Even with only a 1-in-10 chance, this means that there are a lot of homes available in the market.

The relative ease with which the complex molecules needed for life arise, and the suddenness of microbial life first appearing on Earth, suggest that most of these exoplanets may already be occupied. So may our neighbor, Mars. Launched in November 2011, NASA’s Mars rover Curiosity is scheduled to land in August and begin its search for traces of living organisms on the red planet.

As we grapple with the possibility that life has emerged countless times across the universe, does that mean that our unique status is forever lost? Perhaps. But it is also true that in the thousands of millions of years that living creatures have occupied the Earth, it is only in the last hundred thousand or so that a creature capable of asking such questions has existed. In all the cosmos, we may be the only ones who are even vaguely aware of what lies beyond the confines of our rocky, wet world.

As we gaze toward the heavens and marvel about what might be out there, should we not also wonder if there is anyone looking back at us and thinking the very same thing?

• Mark Farmer is a professor and chair of biological sciences at the University of Georgia. His work appears occasionally in the Athens Banner-Herald.